package baidu;

import java.util.ArrayList;
import java.util.Scanner;

//单词接龙
public class WordJieLong {

	static ArrayList<String > list = new ArrayList<String>();
	
	//这种思路还是有bug，比如当输入aba，cbc，ded的时候是连接不起来的，应该是输出No
	//正解： 转换为有向图的欧拉路径 http://www.cnblogs.com/eniac12/p/5584361.html
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int count = 0;
		int wordsCount;
		while(scanner.hasNext()){
			list.clear();
			wordsCount = scanner.nextInt();
			scanner.nextLine();  //用来屏蔽回车键
			for (count = 0; count < wordsCount; count++) {
				list.add(scanner.nextLine());
			}
			canJieLong();
		}
		scanner.close();
//		list.add("abc");
//		list.add("cdeg");
//		list.add("zch");
//		canJieLong();
	}
	public static void canJieLong(){
		int[] front = new int[256];
		int[] rear = new int[256];
		int size = list.size();
		String temp = "";
		char firstChar, lastChar;
		for (int i = 0; i < size; i++) {
			temp = list.get(i);
			if (temp != null) {
				firstChar = temp.charAt(0);
				lastChar = temp.charAt(temp.length() - 1);
				front[firstChar] = front[firstChar] + 1;
				rear[lastChar] = rear[lastChar] + 1;
			}
		}
		
		int difCount = 0;
		for (int i = 'a'; i <= 'z'; i++) {
//			System.out.printf("%c %d次 %d次\n", i , front[i], rear[i]);
			if(Math.abs(front[i] - rear[i]) >= 1){
				difCount++;
			}
		}
		System.out.println(difCount <= 2 ? "YES":"NO");
	}
}
